JPH03290268A - Thermal head - Google Patents

Abstract

PURPOSE:To unify heating temperature distribution of the heating part by a method wherein the title thermal head has a protective layer which is formed by a first part to covet a heating resistor, second parts formed on both sides of the first part and third parts placed outside of the first and second parts, and thermal conductivity for each protective layer is specified. CONSTITUTION:A protective layer consists of a first part 5-1 with thermal conductivity lambda1, second parts 5-2 with thermal conductivity lambda2 and third parts 5-3 with thermal conductivity lambda3, and it is lambda1>lambda2 and lambda3>lambda2. When power is connected to a heating resistor 3, joule heat generated at a heating part 7 is conducted in the protective layer 5-1 and quickly transmitted to the surface of the protective layer 5-1. Since thermal conductivity lambda2 is lower than thermal conductivity lambda1, diffusion of heat generated at the heating part 7 to the protective layer area direction is suppressed, and the surface of the protective layer 5-1 is kept at a sufficient temperature for printing, during pulse power connection. In addition, the thermal head is formed in such a manner that heat conducted in the protective layer 5-2 reaches the protective layer 5-3 at the time of completion of the pulse power connection, and therefore, heat stayed in the protective layers 5-1, 5-2 during the pulse power connection is diffused immediately through the protective layer 5-3 after the completion of the pulse power connection, and the thermal head is quickly cooled to a room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the quality of thermal heads used in thermal recording equipment and the like, and particularly relates to improving the heat generation characteristics of the heat generating portion of the thermal head.

[Summary of the invention]

The function of a thermal head is to transmit Joule heat generated by energizing a heating resistor to a medium such as thermal paper or a thermal transfer ink sheet via a protective layer. Therefore, the thermal properties of the protective layer greatly influence the heat generation/cooling properties of the heat generating part and the heat transfer properties to the media, and through this, they also have a great influence on the print quality of the thermal recording device.

The present invention improves the heat generation and cooling characteristics of the heat generating part by forming part of a single protective layer with low thermal conductivity with a thin film with higher thermal conductivity, thereby improving print quality. It is something that we are trying to improve.

[Conventional technology]

The general structure of the conventional thin-film thermal head heat generating part is explained in the third section.
As shown in the figure. In Fig. 3, 1 is an insulating substrate, 2 is a glaze layer, 3 is a heating resistor, 4 is an electrode, and 5 is a protective layer.
Reference numeral 6 indicates a medium such as thermal paper or a thermal transfer ink sheet, and Joule heat generated by applying a power pulse to the heating resistor 3 is transferred to the medium 6 through the protective layer 5.
The company was in charge of printing the information.

The protective layer 5 is a thin film formed by sputtering, vapor deposition, CVD, etc., and has a thickness of, for example, 6 μm.
m], and its thermal conductivity is low, about 10 [W/mK].

[Problem to be solved by the invention]

However, in conventional thermal heads, the protective layer is formed of a single thin film with low thermal conductivity, so the heat generation and cooling characteristics of the surface of the protective layer are poor, and the heat generation temperature distribution of the heat generating part is also uneven. Since the heat transfer efficiency to the media was also low, satisfactory printing quality could not be obtained.

For example, the heat generation-cooling characteristics at a point 8 corresponding to the center of the heat generating portion 7 on the surface of the protective layer 5 are such that the temperature rise is slower and the cooling characteristics are poorer than the ideal characteristics, as shown in FIG. Furthermore, as shown in FIG. 4, the heat generation temperature distribution of the heat generation portion 7 has a peak at the center of the heat generation portion 7, and a uniform temperature distribution cannot be obtained. Therefore, the printed dots on the medium have a shape as shown in FIG. 5, making it impossible to obtain good printing quality.

[Means to solve the problem]

When considering the issues in obtaining good print quality from the perspective of the thermal characteristics of the heat generating part, the issues can be summarized as follows.

(2) Bringing the heating-cooling characteristics of the surface of the protective layer closer to the ideal profile as shown in Figure 7;

■Make the heat generation temperature distribution uniform within the heat generation dot.

■Improve heat transfer efficiency to the media.

The first thing that can be considered to solve these problems is to use a thin film with high thermal conductivity as a protective layer. The present inventors simulated the heat conduction characteristics of the heat generating portion having the cross-sectional structure shown in FIG. 3 by using the finite element method, and evaluated the effect of the thermal conductivity of the protective layer on the heat generation characteristics. FIG. 6 schematically shows the results. Figure 6(a) shows the protective layer thermal conductivity λ = 2 [W/mK], Figure 6(b) shows the thermal conductivity of the protective layer = 2 =
500 [W/mK], and shows the temperature distribution on the surface of the protective layer 5 at time t when the pulse in the figure is applied. As can be seen from this figure, when the thermal conductivity of the protective layer is high, a sufficient heat generation temperature cannot be obtained. That is, as the thermal conductivity of the protective layer increases, the thermal conductance in the area direction of the protective layer increases, and Joule heat diffuses in the area direction before the surface of the protective layer reaches a sufficient heat generation temperature. Although the surface of the protective layer is expected to have a high heat generation temperature at a very early stage, the amount of heat transferred to the media is small and does not result in color development. Therefore, it can be seen that the above-mentioned problem cannot be achieved as long as the protective layer is formed with a single thermal conductivity.

A second possibility is to replace only the portion of the protective layer directly above the heating resistor with a layer having high thermal conductivity. That is, the purpose is to suppress heat diffusion in the area direction of the protective layer. However, in this case, as shown in Figure 7, the rise in heat generation is expected to be faster and the temperature distribution in the heat generating part is expected to be more uniform, but the cooling characteristics are not the same as in the case of a single low thermal conductivity protective layer. It's exactly the same and no improvement can be expected.

Therefore, in addition to the second structure described above, the present inventors devised a method of providing a portion having high thermal conductivity at an appropriate position in the protective layer in order to further improve the cooling characteristics of the heat generating portion. That is, the above-mentioned second method makes improvements such as speeding up the rise of heat generation, making the temperature distribution uniform, and increasing heat transfer efficiency, and at the same time, the low thermal conductivity portion of the protective layer is transferred to the upper part of the heating resistor. A second high thermal conductivity portion is formed so as to be sandwiched between the first high thermal conductivity portion. By this means, unnecessary heat remaining in the protective layer even after printing can be quickly diffused in the area direction of the protective layer, making it possible to significantly improve cooling characteristics. By these methods, the above ■■
All of the tasks listed in ■ will be accomplished.

As for the formation position of the second high thermal conductivity portion, it is completely possible to specify the optimum formation position by analyzing the heat conduction of the cross section of the heat generating part, including the timing of the printing pulse.

〔Example〕

Embodiments of the present invention will be described based on the drawings. FIG. 1 is a diagram showing an embodiment of the present invention, in which the protective layer includes a first portion 5-1 having a thermal conductivity of λ, a second portion 5-2 having a thermal conductivity of λ2, and a second portion 5-2 having a thermal conductivity of λ2. λ1>λ2 and λ3>λ2. Joule heat generated in the heat generating portion 7 by energizing the heat generating resistor 3 is conducted within the protective layer 5-1- and quickly transmitted to the surface of the protective layer 5-1. At this time, since the thermal conductivity λ2 of the protective layer 5-2 is lower than the thermal conductivity λ1 of the protective layer 5-1, diffusion of the heat generated in the heat generating portion 7 in the area direction of the protective layer is suppressed.
The surface of the protective layer 5-1 is maintained at a temperature sufficient for printing during pulse energization. Further, the protective layer 5-2 is formed so that the heat conducted through the protective layer 5-2 reaches the protective layer 5-3 at the end of pulse energization. As a result, the heat accumulated in the protective layers 5-1 and 5-2 during pulse energization is quickly diffused through the protective layer 5-3 after the pulse energization ends. is rapidly cooled down to room temperature, and the cooling characteristics of the heat generating section 7 are greatly improved.

FIG. 2 illustrates the above action. As shown in FIG. 2, it can be seen that the embodiment shown in FIG. 1 greatly improves the heat generation-cooling characteristics of the heat generating portion, approaching the ideal profile of a rectangle.

FIG. 9 shows a second embodiment of the invention. In the example of FIG. 9, the protective layer 5 having a low thermal conductivity λ2 formed in a conventional manner
A protective layer 5- with a thermal conductivity of λ1 above the heat generating part 7
1 and the thermal conductivity λ formed at the position sandwiching the protective layer 5-1.
It has three protective layers 5-3. Here λ1 > λ2,
λ3>λ2, and the formation position of the protective layer 5-3 is the same as that in FIG. In this example, the high thermal conductivity protective layer 5-1 for improving heat generation characteristics is formed on the top of the protective layer 5, so the heat generation characteristics are slightly deteriorated compared to the example shown in FIG. 1, but λ1>>λ2. By doing so, the impact can be almost ignored. Further, the cooling characteristics are exactly the same as those of the embodiment shown in FIG. 1, and the heat generation-cooling characteristics are greatly improved as shown in FIG. Furthermore, in this embodiment, the difference in the surface of the protective layer 5 caused by the difference in the electrode 4 is flattened by the protective layer 5-1, so the pressure contact condition with media such as thermal paper and thermal transfer ink sheets is also improved. It also has the excellent effect of significantly improving heat transfer efficiency.

In the present invention, by setting λ1>>λ2 and λ3>>λ2, the effect of improving heat generation-cooling characteristics is further increased. Moreover, if λ1=λ3, that is, the protective layer 5-1 and the protective layer 5-3 are formed of the same material, the manufacturing process can be simplified.

〔Effect of the invention〕

As described above, according to the present invention, the heat generation-cooling characteristics of the thermal head heat generating section can be brought close to the ideal rectangular profile, and the heat generation temperature distribution of the heat generating section can also be made uniform, so that printing It is possible to improve the dot shape to a nearly rectangular shape and significantly improve print quality. In addition, heat generation efficiency is improved, making it possible to lower the power consumption of the thermal head.Furthermore, the cooling characteristics are improved, increasing printing speed, which was previously subject to major limitations due to heat accumulation in the heat generating part. It is also possible to bring about

[Brief explanation of the drawing]

1 and 9 are sectional views showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing heat generation-cooling characteristics in the embodiment. FIG. 3 is a sectional view showing the general structure of a conventional thermal head heat generating section, FIG. 4 is an explanatory drawing showing the temperature distribution of the heat generating section, and FIG. 5 is an explanatory drawing showing the shape of printed dots. 6(a) and 6(b) are explanatory diagrams showing the heat generation temperature distribution when the thermal conductivity of the protective layer is different in the conventional structure, and FIG. 7 is an explanatory diagram showing the heat generation-cooling characteristics of the heat generating part of the thermal head. 8 are explanatory diagrams showing the characteristics when a high thermal conductivity protective layer is formed only directly above the heat generating part. 1 ・ ・ 21 3 ・ ・ 4 ・ ・ 5, 5 6 Fight 7 ・ ・ 8 ・ ・ ・Insulating substrate, glaze layer, heating resistor, electrode 1.5-2.5 ・Protective layer, printing media, heat generation Center of section/center of protective layer surface

Claims (1)

[Claims] In a thermal head comprising an insulating substrate, a glaze layer, a heating resistor, an electrode for energizing the heating resistor, and a protective layer formed to cover the heating resistor including the electrode, a first portion formed directly above and having a thermal conductivity λ_1 that should cover at least the heating resistor; and a thermal conductivity formed on both sides of the first portion in parallel to the arrangement direction of the heating resistor. A third portion sandwiching the first and second portions and having a thermal conductivity of λ_3 is formed in parallel to the arrangement direction of the heating resistors. has a protective layer, and the thermal conductivity of the protective layer is λ_1>λ_2
A thermal head characterized in that λ_3>λ_2.